Ultrasonic-assisted in situ synthesis and characterization of superparamagnetic Fe3O4 nanoparticles

Superparamagnetic Fe₃O₄ nanoparticles were synthesized via a modified coprecipitation method, and were characterized with X-ray diffraction (XRD), vibrating sample magnetometer (VSM), Zeta potential and FT-IR, respectively. The influences of different kinds of surfactants (sodium dodecyl benzene sulfonate, polyethyleneglycol, oleic acid and dextran), temperatures and pH values on the grain size and properties were also investigated. In this method, Fe³⁺ was used as the only Fe source and partially reduced to Fe²⁺ by the reducing agent with precise content. The following reaction between Fe³⁺, Fe²⁺ and hydroxide radical brought pure Fe₃O₄ nanoparticles. The tiny fresh nanoparticles were coated in situ with surfactant under the action of sonication. Comparing with uncoated sample, the mean grain size and saturation magnetization of coated Fe₃O₄ nanoparticles decrease from 18.4 nm to 5.9-9.0 nm, and from 63.89 emu g⁻¹ to 52-58 emu g⁻¹ respectively. When oleic was used as the surfactant, the mean grain size of Fe₃O₄ nanoparticles firstly decreases with the increase of reaction temperature, but when the temperature is exceed to 80 °C, the continuous increase of temperature resulted in larger nanoparticles. the grain size decreases gradually with the increasing of pH values, and it remains unchanged when the PH value is up to 11. The saturation magnetization of as-prepared Fe₃O₄ nanoparticles always decreases with the fall of grain size.     

Low temperature synthesis of Fe3O4 micro-spheres and its application in lithium ion battery

Fe₃O₄ micro-spheres with nanoparticles close-packed architectures were synthesized via a simple chemical method using (NH₄)₂Fe(SO₄)₂·6H₂O, hexamethylenetetramine, and NaF as reaction materials. This chemical synthesis took place in a vitreous jar under low temperature (90 °C) and atmospheric pressure. The morphology and structure of the as-synthesized products were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Raman spectrum. Electrochemical properties of the as-synthesized Fe₃O₄ micro-spheres as anode electrode of lithium ion batteries were studied by conventional charge/discharge tests, which exhibit steady charge/discharge platforms at different current densities. The as-prepared Fe₃O₄ electrode shows high initial discharge capacity of 1166 and 1082 mAh g⁻¹ at current density of 0.05 and 0.1 mA cm⁻², respectively.     

Preparation, structure and electrical conductivity of the pyrochlore-type phase Sm2Zr2O7 codoped with bivalent magnesium and trivalent dysprosium cations

The pyrochlore-type phases with the compositions of SmDy_1−xMg_xZr₂O_7−x/2 (0 ≤ x ≤ 0.20) have been prepared by pressureless-sintering method for the first time as possible solid electrolytes. The structure and electrical conductivity of SmDy_1−xMg_xZr₂O_7−x/2 ceramics have been studied by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance spectroscopy measurements. SmDy_1−xMg_xZr₂O_7−x/2 (x = 0, 0.05, 0.10) ceramics exhibit a single phase of pyrochlore-type structure, and SmDy_1−xMg_xZr₂O_7−x/2 (x = 0.15, 0.20) ceramics consist of pyrochlore phase and a small amount of the second phase magnesia. The total conductivity of SmDy_1−xMg_xZr₂O_7−x/2 ceramics obeys the Arrhenius relation, and the total conductivity of each composition increases with increasing temperature from 673 to 1173 K. SmDy_1−xMg_xZr₂O_7−x/2 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10⁻⁴ to 1.0 atm at all test temperature levels. The highest total conductivity value is about 8 × 10⁻³ S cm⁻¹ at 1173 K for SmDy_1−xMg_xZr₂O_7−x/2 ceramics.     

In situ synthesis of Co3O4/graphene nanocomposite material for lithium-ion batteries and supercapacitors with high capacity and supercapacitance

Co₃O₄/graphene nanocomposite material was prepared by an in situ solution-based method under reflux conditions. In this reaction progress, Co²⁺ salts were converted to Co₃O₄ nanoparticles which were simultaneously inserted into the graphene layers, upon the reduction of graphite oxide to graphene. The prepared material consists of uniform Co₃O₄ nanoparticles (15-25 nm), which are well dispersed on the surfaces of graphene nanosheets. This has been confirmed through observations by field emission scanning electron microscopy, transmission electron microscopy and atomic force microscopy. The prepared composite material exhibits an initial reversible lithium storage capacity of 722 mAh g⁻¹ in lithium-ion cells and a specific supercapacitance of 478 F g⁻¹ in 2 M KOH electrolyte for supercapacitors, which were higher than that of the previously reported pure graphene nanosheets and Co₃O₄ nanoparticles. Co₃O₄/graphene nanocomposite material demonstrated an excellent electrochemical performance as an anode material for reversible lithium storage in lithium ion cells and as an electrode material in supercapacitors.     

Studies on the power factor of (Ba,Sr)Co2+xRu4−xO11 compounds

We have prepared polycrystalline single-phase ACo_2+xRu_4−xO₁₁ (A = Sr, Ba; 0 ≤ x ≤ 0.5) using the ceramic method and we have studied their structure, electrical resistivity and Seebeck coefficient, in order to estimate their power factor (P.F.). These layered compounds show values of electrical resistivity of the order of 10⁻⁵ Ωm and their Seebeck coefficients are positive and range from 1 μV K⁻¹ (T = 100 K) to 20 μV K⁻¹ (T = 450 K). The maximum power factor at room temperature is displayed by BaCo₂Ru₄O₁₁ (P.F.: 0.20 μW K⁻² cm⁻¹), value that is comparable to that shown by compounds such as SrRuO₃ and Sr₆Co₅O₁₅.     

A literature review and test: Structure and physicochemical properties of spinel LiMn2O4 synthesized by different temperatures for lithium ion battery

A series of LiMn₂O₄ spinel was prepared by adipic acid-assisted sol–gel method at different temperatures. The structure and physicochemical properties of spinel LiMn₂O₄ synthesized by different temperatures were investigated by differential thermal analysis (DTA) and thermogravimetery (TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron micrographs (SEM), inductively coupled plasma-mass spectroscopy (ICP-MS), galvanostatic charge–discharge test, and cyclic voltammetry (CV), respectively. TG–DTA shows that the weight loss occurs in four temperature regions during the synthesis of LiMn₂O₄. XRD indicates that the sintering temperature affects the formation of spinel phase, and prominent LiMn₂O₄ spinel powder with smaller atom location confusion forms about 800 °C. XPS reveals that the manganese oxidation state in spinel lithium manganese oxide synthesized at different temperatures is between +3 and +4. SEM shows that LiMn₂O₄ spinel synthesized at 800 °C has the uniform, nearly cubic structure morphology with narrow size distribution. ICP-MS indicates that the average chemical valence of Mn element of LiMn₂O₄ synthesized at 800 °C is the most close to 3.5 among the samples synthesized at different temperatures. CV illustrates that the LiMn₂O₄ synthesized at 800 °C has the best electrochemical activity. Charge–discharge test explains that the capacity retention sintered at 350, 700 and 800 °C over the first 50 cycles is 93.6%, 86.1% and 85.2%, respectively, but the discharge capacity at the 50th cycle is 82.2, 104.8 and 110.8 mAh g⁻¹, respectively.     

Structural and dielectric properties of Bi2Zn2/3Nb4/3O7 thin films prepared by pulsed laser deposition at low temperature for embedded capacitor applications

Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited on Pt/TiO₂/SiO₂/Si(1 0 0) substrates at a room temperature under the oxygen pressure of 1-10 Pa by pulsed laser deposition. Bi₂Zn_2/3Nb_4/3O₇ thin films were then post-annealed below 200 °C in a rapid thermal process furnace in air for 20 min. The dielectric and leakage current properties of Bi₂Zn_2/3Nb_4/3O₇ thin films are strongly influenced by the oxygen pressure during deposition and the post-annealing temperature. Bi₂Zn_2/3Nb_4/3O₇ thin films deposited under 1 Pa oxygen pressure and then post-annealed at a temperature of 150 °C show uniform surface morphologies. Dielectric constant and loss tangent are 57 and 0.005 at 10 kHz, respectively. The high resolution TEM image and the electron diffraction pattern show that nano crystallites exist in the amorphous thin film, which may be the origin of high dielectric constant in the Bi₂Zn_2/3Nb_4/3O₇ thin films deposited at low temperatures. Moreover, Bi₂Zn_2/3Nb_4/3O₇ thin film exhibits the excellent leakage current characteristics with a high breakdown strength and the leakage current density is approximately 1 × 10⁻⁷ A/cm² at an applied bias field of 300 kV/cm. Bi₂Zn_2/3Nb_4/3O₇ thin films are potential materials for embedded capacitor applications.     

Synthesis of lanthanum carbonate nanoparticles via sonochemical method for preparation of lanthanum hydroxide and lanthanum oxide nanoparticles

Lanthanum carbonate nanoparticles were synthesized from the reaction of lanthanum acetate and Na₂CO₃ under sonication via sonochemical method. Lanthanum hydroxide nanoparticles were prepared by facial hydrothermal processing from the resulted product at 110 °C for 24 h. The role of surfactant, calcination temperature and sonication time were investigated on the morphology and particle size of the products. Products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectrum (XPS), and Fourier transform infrared (FT-IR) spectra. La₂O₃ nanoparticles were obtained by calcinations of the nanoparticles of lanthanum carbonate at 600 °C.     

Effect of Cr7C3 on the mechanical, thermal, and electrical properties of Cr2AlC

In this work, phase pure Cr₂AlC and impure Cr₂AlC with Cr₇C₃ have been fabricated to investigate the mechanical, thermal, and electrical properties. The thermal expansion coefficient is determined as 1.25 × 10⁻⁵ K⁻¹ in the temperature range of 25-1200 °C. The thermal conductivity of the Cr₂AlC is 15.73 W/m K when it is measured at 200 °C. With increasing temperature from 25 °C to 900 °C, the electrical conductivity of Cr₂AlC decreases from 1.8 × 10⁶ Ω⁻¹ m⁻¹ to 5.6 × 10⁵ Ω⁻¹ m⁻¹. For the impure phase of Cr₇C₃, it has a strengthening and embrittlement effect on the bulk Cr₂AlC. And the Cr₂AlC with Cr₇C₃ would result in a lower high-temperature thermal expansion coefficient, thermal conductivity, specific heat capacity and electrical conductivity.     

The effects of temperature and composition on the thermal conductivities of [(ZrO2)1−x(CeO2)x]0.92(Y2O3)0.08 (0 ? x ? 1) solid solutions

The thermal conductivities of [(ZrO₂)_1−x(CeO₂)_x]_0.92(Y₂O₃)_0.08 (0 ? x ? 1) solid solutions are studied in this paper. The incorporation of ZrO₂ and CeO₂ in the solid solution decreases the thermal conductivity compared with their end members (YSZ and YDC). The thermal conductivities of the solid solutions show clearly different temperature dependences in the ZrO₂-rich (0 ? x ? 0.5) region and in the CeO₂-rich region (0.5 ? x ? 1). The composition and the temperature dependence of the thermal conductivities are discussed based on established phonon scattering theories. We have concluded that the composition dependence of the thermal conductivity of this system is mainly controlled by the mass difference between Zr⁴⁺ and Ce⁴⁺, while the thermal conductivity-temperature relationship is dominated by the randomness of the defect distribution.     

Combustion synthesis of CaSc2O4:Ce nano-phosphors in a closed system

The CaSc₂O₄:Ce³⁺ nano-phosphors were successfully prepared by a single-step combustion method at an ignition temperature as low as 200 °C in a closed autoclave using glycine as a fuel and PEG4000 as a dispersant. The samples were characterized by X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscope (TEM). The results revealed that CaSc₂O₄:Ce³⁺ nano-phosphors can be conveniently prepared at an ignition temperature as low as 200 °C, which was much lower than that in the ordinary combustion methods. The optimized ignition temperature was 220 °C. The CaSc₂O₄:Ce³⁺ nano-phosphors give a uniform particle size in the range of 15-20 nm. The low ignition temperature and the addition of PEG4000 dispersant play important roles in the formation of small sized nanoparticles. The as-prepared nano-phosphors were incompact aggregates, but highly dispersed nano-phosphors can be obtained after further ultrasonic treatment. The CaSc₂O₄:Ce³⁺ nano-phosphors give satisfactory luminescence characteristic benefiting from the closed circumstance, in which cerium atoms can be isolated from the oxidizing atmosphere and non-fluorescent Ce⁴⁺ ions can be ruled out. The present highly dispersed CaSc₂O₄:Ce³⁺ nano-phosphors with efficient fluorescence are promising in the field of biological labeling, and the present low temperature combustion method is facile and convenient and can be applied as a universal process for preparing non-aggregate oxide nano-phosphors, especially those being sensitive to air at high temperature.     

Sol-gel synthesis and electrochemical performance of Li4Ti5O12/graphene composite anode for lithium-ion batteries

Li₄Ti₅O₁₂/graphene composite was prepared by a facile sol-gel method. The lattice structure and morphology of the composite were investigated by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The electrochemical performances of the electrodes have been investigated compared with the pristine Li₄Ti₅O₁₂ synthesized by a similar route. The Li₄Ti₅O₁₂/graphene composite presents a higher capacity and better cycling performance than Li₄Ti₅O₁₂ at the cutoff of 2.5-1.0 V, especially at high current rate. The excellent electrochemical performance of Li₄Ti₅O₁₂/graphene electrode could be attributed to the improvement of electronic conductivity from the graphene sheets. When discharged to 0 V, the Li₄Ti₅O₁₂/graphene composite exhibited a quite high capacity over 274 mAh g⁻¹ below 1.0 V, which was quite beneficial for not only the high energy density but also the safety characteristic of lithium-ion batteries.     

Synthesis and electrochemical properties of porous LiV3O8 as cathode materials for lithium-ion batteries

In this paper, we report on the synthesis of porous LiV₃O₈ by using a tartaric acid-assisted sol-gel process and their enhanced electrochemical properties for reversible lithium storage. The crystal structure, morphology and pore texture of the as-synthesized samples are characterized by means of XRD, SEM, TEM/HRTEM and N₂ adsorption/desorption measurements. The results show that the tartaric acid plays a pore-making function and the calcination temperature is an important influential factor to the pore texture. In particular, the porous LiV₃O₈ calcined at 300 °C (LiV₃O₈-300) exhibits hierarchical porous structure with high surface area of 152.4 m² g⁻¹. The electrochemical performance of the as-prepared porous LiV₃O₈ as cathode materials for lithium ion batteries is investigated by galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy. The porous LiV₃O₈-300 displays a maximum discharge capacity of 320 mAh g⁻¹ and remains 96.3% of its initial discharge capacity after 50 charge/discharge cycles at the current density of 40 mA g⁻¹ due to the enhanced charge transfer kinetics with a low apparent activity energy of 35.2 kJ mol⁻¹, suggesting its promising application as the cathode material of Li-ion batteries.     

Thermoelectric properties of Bi2SexTe3−x prepared by Bridgman method

Bi₂Se_xTe_3−x crystals with various x values were grown by Bridgman method. The electrical conductivity, σ, was found to decrease with increasing Se content. The highest σ of 1.6 × 10⁵ S m⁻¹ at room temperature was reached at x = 0.12 with a growth rate of 0.8 mm h⁻¹. The Seebeck coefficient, S, was less dependent on Se content, all with positive values showing p-type characteristics, and the highest S was measured to be 240 μV K⁻¹ at x = 0.24. The lowest thermal conductivity, κ, was 0.7 W m⁻¹ K⁻¹ at x = 0.36. The electronic part of κ, κ_el, showed a decrease with increasing Se content, which implies that the hole concentration as the main carriers was reduced by the addition of Se. The highest dimensionless figure of merit, ZT, at room temperature was 1.2 at x = 0.36, which is attributed to the combination of a rather high electrical conductivity and Seebeck coefficient and low thermal conductivity.     

Thermoelectric properties of Cu1−xPtxFeO2 (0.0 ≤ x ≤ 0.05) delafossite-type transition oxide

The samples of Cu_1−xPt_xFeO₂ (0 ≤ x ≤ 0.05) delafossite were synthesized by solid state reaction method for studying thermoelectric properties. The properties of Seebeck coefficient, electrical conductivity and thermal conductivity were measured in the high temperature ranging from 300 to 960 K. The results of Seebeck coefficient, electrical conductivity and power factor were increased with increasing Pt substitution and temperature. The thermal conductivity was decreased from 5.8 to 3.5 W/mK with increasing the temperature from 300 to 960 K. An important results, the highest value of power factor and ZT is 2.0 × 10⁻⁴ W/mK² and 0.05, respectively, for x = 0.05 at 960 K.     

Electrical and thermal characterization of Sm doped ceria electrolytes synthesized by combustion technique

Nanocrystalline samarium doped ceria electrolyte [Ce_0.9Sm_0.1O_1.95] was synthesized by citrate gel combustion technique involving mixtures of cerium nitrate oxidizer (O) and citric acid fuel (F) taken in the ratio of O/F = 1. The as-combusted precursors were calcined at 700 °C/2 h to obtain fully crystalline ceria nano particles. It was further made into cylindrical pellets by compaction and sintered at 1200 °C with different soaking periods of 2, 4 and 6 h. The sintered ceria was characterized for the microstructures, electrical conductivity, thermal conductivity and thermal diffusivity properties. In addition, the combustion derived ceria powder was also analysed for the crystallinity, BET surface area, particle size and powder morphology. Sintered ceria samples attained nearly 98% of the theoretical density at 1200 °C/6 h. The sintered microstructures exhibit dense ceria grains of size less than 500 nm. The electrical conductivity measurements showed the conductivity value of the order of 10⁻² S cm⁻¹ at 600 °C with activation energy of 0.84 eV between the temperatures 100 and 650 °C for ceria samples sintered at 1200 °C for 6 h. The room temperature thermal diffusivity and thermal conductivity values were determined as 0.5 × 10⁻⁶ m² s⁻¹ and 1.2 W m⁻¹ K⁻¹, respectively.     

Oxidation of Cr2AlC coatings in the temperature range of 1230 to 1410 °C

The isothermal oxidation behavior of Cr₂AlC coatings on alumina substrates was investigated in the temperature range of 1230 to 1410 °C. The structure, surface morphology, microstructure evolution and chemistry of the reaction products have been investigated. In the investigated temperature range, the Cr₂AlC films form a dense continuous oxide scale consisting of α-Al₂O₃ on Cr carbides. The oxidation rates determined by thermo gravimetric analysis (TGA) were parabolic, indicating that diffusion through the scale is the rate limiting mechanism. The activation energy for oxidation was determined to be 348 kJ mol^− 1 and the parabolic rate constant at 1230 °C was 7.1 × 10^− 10 kg² m^− 4 s^− 1. Hence, the oxidation behavior is comparable to NiAl in the temperature range and time intervals investigated. With increasing oxidation time voids form at the interface between oxide and Cr carbides and the amount of Cr₇C₃ increases at the expense of Cr₃C₂. Based on our thermodynamic calculations the oxygen partial pressure below the oxide scale increases as Al is depleted and Cr carbides oxidize, resulting in CO gas- and Cr₂O₃-formation. The formation of gas may together with the depletion of Al and Cr lead to the significant void formation observed in the Cr carbide interlayer. Observation of both Cr carbide precipitates and the formation of (Al,Cr)₂O₃ solid solution support this notion. For comparison bulk Cr₂AlC was oxidized. It is argued that the absence of pores in oxidized bulk Cr₂AlC is due to the considerably larger amount of Al available.     

Charge compensation, electrical and dielectric behavior of lanthanum doped CaCu3Ti4O12

Mechanism of charge compensation on lanthanum, (La³⁺) substitution on Ca site in calcium copper titanate (CaCu₃Ti₄O₁₂), and its effect on resulting electrical and dielectric properties has been studied in the present investigation. For this purpose samples were prepared according to two stoichiometries viz. La_xCa_(1−3x/2)Cu₃Ti₄O₁₂ (x ≤ 0.09) and La_xCa_(1−x)Cu₃Ti₄O₁₂ (x = 0.03) by solid state ceramic route. The former represents ionic compensation while the later is in accordance with electronic compensation. Nature of charge carriers is identified by measuring Seebeck coefficient which is found to be negative in the entire range of measurement. In order to understand the mechanism of conduction, ac conductivity is measured as a function of temperature and frequency. Space charge polarization is the dominant polarization mechanism phenomenon at low frequency and high temperature while orientation polarization dominates at low temperature and high frequency. Impedance analysis confirms the formation of internal barrier layers which is responsible for high dielectric constant in these samples.     

Effects of Mg substitution on the structural, optical, and electrical properties of CuAlO2 thin films

Mg-doped CuAlO₂ thin films are prepared by the chemical solution method. The XRD results show that the solid solubility of Mg species on Al sites in CuAlO₂ lattice is lower than 2 at.%. When less than 2 at.% of Mg is added to the CuAlO₂ film, the surface roughness of the films was reduced with Mg substitution. Moreover, the c-axis orientation of the films improves because the in-plane fusion between CuAlO₂ crystallites is hindered. Optical and electrical measurements show that substituting Al³⁺ in the films with Mg²⁺ increases both their transmittance in the visible region and their optical band gaps. As well, their electrical conductivity is enhanced. At 300 K, the conductivity of the 1 at.% Mg-doped sample is up to 5.2 × 10⁻³ S/cm. Thus, Mg-doped CuAlO₂ films may have potential applications as transparent conductive oxides.     

Combustion synthesis and characterization of highly crystalline single phase nickel ferrite nanoparticles

A combustion route of synthesizing highly crystalline single phase nickel ferrite (NiFe₂O₄) spinel nanoparticles using various amounts of dl-alanine as fuel has been reported in this paper. The role of the amount of fuel is found to be significant in the size control and phase purity of nano crystalline samples. The structural, thermal, morphological and magnetic studies have been carried out. XRD patterns reveal the formation of highly crystalline nano NiFe₂O₄ with high degree of phase purity when fuel concentration is maintained at 1 M and 2 M. FTIR spectra also prove the formation of pure nano NiFe₂O₄. The temperature and fuel effects are found to have strong influence on size, structural, and magnetic properties of materials. The magnetic measurements show that the nano NiFe₂O₄ samples exhibit soft ferromagnetism with the highest saturation magnetization Ms at room temperature as 42.53 emu/g.